Combined Effect of Free-Stream Turbulence and Unsteady Wake on Heat Transfer Coefficients From a Gas Turbine Blade

1995 ◽  
Vol 117 (2) ◽  
pp. 296-302 ◽  
Author(s):  
L. Zhang ◽  
J.-C. Han
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Combined Effect ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake ◽  
Turbulence Grid

The combined effect of free-stream turbulence and unsteady wakes on turbine blade surface heat transfer was studied. The experiments used a five-blade linear cascade in a low-speed wind tunnel facility. A turbulence grid and spoked-wheel type wake generator produced the free-stream turbulence and unsteady wakes. The mainstream Reynolds numbers based on the cascade inlet mean velocity and blade chord length were 100,000, 200,000, and 300,000. Results show that the blade time-averaged heat transfer coefficient depends on the mean turbulence intensity, regardless of whether this mean turbulence intensity is from unsteady wake only, turbulence grid only, or a wake and grid combination. The higher mean turbulence promotes earlier boundary layer transition and causes much higher heat transfer coefficients on the suction surface. It also significantly enhances the heat transfer coefficients on the pressure surface. The unsteady wake greatly affects blade heat transfer for low oncoming free-stream turbulence; however, the wake effect diminishes for high oncoming turbulence. The free-stream turbulence also strongly affects blade heat transfer for a low wake passing frequency, but the oncoming turbulence effect diminishes for a high unsteady wake condition.

Unsteady Wake Effect on Film Effectiveness and Heat Transfer Coefficient From a Turbine Blade With One Row of Air and CO2 Film Injection

1994 ◽  
Vol 116 (4) ◽  
pp. 921-928 ◽  
Author(s):  
S. Ou ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Strouhal Number ◽  
Turbine Blade ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Wake Effect ◽  
Pressure Surface ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake

The effect of unsteady wake and film injection on heat transfer coefficients and film effectiveness from a gas turbine blade was found experimentally. A spoked wheel type wake generator produced the unsteady flow. Experiments were done with a five airfoil linear cascades in a low-speed wind tunnel at a chord Reynolds number of 3 × 105, two wake Strouhal numbers of 0.1 and 0.3, and a no-wake case. A model turbine blade injected air or CO2 through one row of film holes each on the pressure and suction surfaces. The results show that the large-density injectant (CO2) causes higher heat transfer coefficients on the suction surface and lower heat transfer coefficients on the pressure surface. At the higher blowing ratios of 1.0 and 1.5, the film effectiveness increases with increasing injectant-to-mainstream density ratio at a given Strouhal number. However, the density ratio effect on film effectiveness is reversed at the lowest blowing ratio of 0.5. Higher wake Strouhal numbers enhance the heat transfer coefficients but reduce film effectiveness for both density ratio injectants at all three blowing ratios. The effect of the wake Strouhal number on the heat transfer coefficients on the suction surface is greater than that on the pressure surface.

Simulation of Heat Transfer From Flow With High Free-Stream Turbulence to Turbine Blades

1997 ◽  
Vol 119 (2) ◽  
pp. 284-291 ◽  
Author(s):  
E. Fridman
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Turbine Blades ◽  
Plate Boundary ◽  
Transfer Coefficients ◽  
Relaxation Length ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients ◽  
High Level ◽  
Flat Plate Boundary Layer

The present investigation is devoted to one of the most difficult problems in the gas turbine industry: predicting the heat transfer to turbine blades. It is known that one of the important factors that affects heat transfer coefficients is a significant level of turbulence in the flow that surrounds a turbine blade. The influence of free-stream turbulence on heat transfer coefficients for a flat plate boundary layer with zero pressure gradient or in the vicinity of the stagnation point of a circular cylinder is investigated numerically. An algebraic relaxation-length model of turbulence is applied in order to simulate real situations in flows with a high level of free-stream turbulence. The results, temperature and velocity profiles, and heat transfer and drag coefficients, are compared with available experimental data. The proposed method is recommended for practical calculations of heat transfer coefficients on turbine blades.

Combined Effect of Grid Turbulence and Unsteady Wake on Film Effectiveness and Heat Transfer Coefficient of a Gas Turbine Blade With Air and CO2 Film Injection

1997 ◽  
Vol 119 (3) ◽  
pp. 594-600 ◽  
Author(s):  
S. V. Ekkad ◽  
A. B. Mehendale ◽  
J. C. Han ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Leading Edge ◽  
Combined Effect ◽  
Grid Turbulence ◽  
Free Stream Turbulence ◽  
Nusselt Numbers ◽  
Unsteady Wake

Experiments were performed to study the combined effect of grid turbulence and unsteady wake on film effectiveness and heat transfer coefficient of a turbine blade model. Tests were done on a five-blade linear cascade at the chord Reynolds number of 3.0 × 105 at cascade inlet. Several combinations of turbulence grids, their locations, and unsteady wake strengths were used to generate various upstream turbulence conditions. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Air and CO2 were used as injectants. Results show that Nusselt numbers for a blade with film injection are much higher than that without film holes. An increase in mainstream turbulence level causes an increase in Nusselt numbers and a decrease in film effectiveness over most of the blade surface, for both density injectants, and at all blowing ratios. A free-stream turbulence superimposed on an unsteady wake significantly affects Nusselt numbers and film effectiveness compared with only an unsteady wake condition.

The Influence of Free Stream Turbulence on the Local Heat Transfer From Cylinders

1960 ◽  
Vol 82 (2) ◽  
pp. 101-107 ◽  
Author(s):  
R. A. Seban
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Intensity ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients

Local heat-transfer coefficients and recovery factors are presented for three different cylinders in a two-dimensional subsonic air flow, with emphasis on the effect of screen-produced turbulence on these quantities. The increase in turbulent intensity so realized produced larger local heat-transfer coefficients, in a way dependent upon the location on the cylinders, through a direct increase in the heat transfer to the laminar boundary layer, through an earlier transition to turbulence, or through an alteration in the character of the separated flow. Alternatively, recovery factors were affected less, being invariant with respect to the turbulent intensity for attached boundary layer flow, but demonstrating large changes in those separated flow regions for which increased free stream turbulence produced substantial changes in the nature of the separated flow.

Influence of Unsteady Wake on Heat Transfer Coefficient From a Gas Turbine Blade

1993 ◽  
Vol 115 (4) ◽  
pp. 904-911 ◽  
Author(s):  
J.-C. Han ◽  
L. Zhang ◽  
S. Ou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Strouhal Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake ◽  
Wake Passing

The effect of unsteady wake on surface heat transfer coefficients of a gas turbine blade was experimentally determined using a spoked wheel type wake generator. The experiments were performed with a five-airfoil linear cascade in a low-speed wind tunnel facility. The cascade inlet Reynolds number based on the blade chord was varied from 1 to 3 × 105. The wake Strouhal number was varied between 0 and 1.6 by changing the rotating wake passing frequency (rod speed and rod number), rod diameter, and cascade inlet velocity. A hot-wire anemometer system was located at the cascade inlet to detect the instantaneous velocity, phase-averaged mean velocity, and turbulence intensity induced by the passing wake. A thin foil thermocouple instrumented blade was used to determine the surface heat transfer coefficients. The results show that the unsteady passing wake promotes earlier and broader boundary layer transition and causes much higher heat transfer coefficients on the suction surface, whereas the passing wake also significantly enhances heat transfer coefficients on the pressure surface. The blade heat transfer coefficients for a given Reynolds number flow increase with the wake Strouhal number by increasing the rod speed, rod number, or rod diameter. For a given wake passing frequency and rod diameter, the blade heat transfer coefficients decrease with decreasing Reynolds number, although the corresponding wake Strouhal number is increased. The results suggest that both the Reynolds and Strouhal numbers are important parameters in determining the blade heat transfer coefficients in unsteady wake flow conditions.

Effect of Unsteady Wake With Trailing Edge Coolant Ejection on Film Cooling Performance for a Gas Turbine Blade

1998 ◽  
Author(s):  
Hui Du ◽  
Srinath V. Ekkad ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Film Cooling ◽  
Surface Heat ◽  
Blade Surface ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Surface Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake

The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coefficient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear cascade. The coolant jet ejection is simulated by ejecting coolant through holes on the hollow spokes of the wake generator. For a blade without film holes, unsteady wake increases both pressure side and suction side heat transfer levels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coefficients particularly near the leading edge region. For a film-cooled blade, unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ejection to the unsteady wake has a small effect on surface heat transfer coefficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients.

Effect of Unsteady Wake With Trailing Edge Coolant Ejection on Film Cooling Performance for a Gas Turbine Blade

1999 ◽  
Vol 121 (3) ◽  
pp. 448-455 ◽  
Author(s):  
H. Du ◽  
S. V. Ekkad ◽  
J.-C. Han
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Film Cooling ◽  
Surface Heat ◽  
Blade Surface ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Surface Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake

The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coefficient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear cascade. The coolant jet ejection is simulated by ejecting coolant through holes on the hollow spokes of the wake generator. For a blade without film holes, unsteady wake increases both pressure side and suction side heat transfer levels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coefficients particularly near the leading edge region. For a film-cooled blade, unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ejection to the unsteady wake has a small effect on surface heat transfer coefficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

Heat Transfer Coefficients and Film Cooling Effectiveness on the Squealer Tip of a Gas Turbine Blade

2003 ◽  
Vol 125 (4) ◽  
pp. 648-657 ◽  
Author(s):  
Jae Su Kwak ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Rotor Blade ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio

Experimental investigations were performed to measure the detailed heat transfer coefficients and film cooling effectiveness on the squealer tip of a gas turbine blade in a five-bladed linear cascade. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The test blade had a squealer (recessed) tip with a 4.22% recess. The blade model was equipped with a single row of film cooling holes on the pressure side near the tip region and the tip surface along the camber line. Hue detection based transient liquid crystals technique was used to measure heat transfer coefficients and film cooling effectiveness. All measurements were done for the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span at the two blowing ratios of 1.0 and 2.0. The Reynolds number based on cascade exit velocity and axial chord length was 1.1×106 and the total turning angle of the blade was 97.9 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. Results showed that the overall heat transfer coefficients increased with increasing tip gap clearance, but decreased with increasing blowing ratio. However, the overall film cooling effectiveness increased with increasing blowing ratio. Results also showed that the overall film cooling effectiveness increased but heat transfer coefficients decreased for the squealer tip when compared to the plane tip at the same tip gap clearance and blowing ratio conditions.

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